Functionality question for several Dungeoneer cards

Sever Cards Like Fire Bomb, Infernal Arcana, Frostbound Celestial and so on. State: Discard this card as an instant or response in order to get some effect. The question is: can i discard those cards from my hand in order for them to have the stated effect, if so can i do it without the printed glory/peril cost. The 2.2 Version of the rules states card appears only if the card is played and paid for with glory/peril, if so how could one for example play a card like Skeletal Iceman for one less Peril if its ability is available only after i already paid its cost?

Card effects take effect the moment they are played.

I can see an error here.

I play a card. Effect is first. Then i pay a cost. So at the moment I paid for the card, the effect is alredy working.

What is happening when somebody plays a card that says: "Discard [some card] before it takes effect" ???

Do I pay discarded card cost or not?

Your first assumption is incorrect a card effect is not before it is paid for. A card has no effect until its cost is paid. A card is not in play until its cost is paid.